Poly(trimethylene carbonate) (PTMC) is an aliphatic polycarbonate synthesized from the 6-membered cyclic carbonate,

trimethylene carbonate Trimethylene carbonate, or 1,3-propylene carbonate, is a 6-membered cyclic carbonate ester. It is a colourless solid that upon heating or catalytic ring-opening converts to poly(trimethylene carbonate) (PTMC). Such polymers are called aliphatic p ...

(1,3-propylene carbonate or 1,3-Dioxan-2-one). Trimethylene carbonate (TMC) is a colorless crystalline solid with melting point ranging between 45°C and 48 °C and boiling point at 255ºC (at 760 mmHg). TMC is originally synthesized from 1,3-propanediol with phosgene or carbon monoxide, which are highly poisonous gases. Another route is from the transesterification of 1,3-propanediol and dialkylcarbonates. This route is considered "greener" compared to the other one, since precursors can be obtained from renewable resources and carbon dioxide.

Synthesis

In opposition to five-membered cyclic carbonate, the six-membered ones like trimethylene carbonate are thermodynamically less stable than its polymer, undergoing the ring-opening polymerization with retention of CO

_2

in the polymer structure, and generation an aliphatic polycarbonate. TCM polymerization

Ring-opening polymerization In polymer chemistry, ring-opening polymerization (ROP) is a form of chain-growth polymerization, in which the terminus of a polymer chain attacks cyclic monomers to form a longer polymer (see figure). The reactive center can be radical, anion ...

(ROP) is the most common method used to synthesize poly(trimethylene carbonate) and their copolymers, since this synthetic route can allow mild reaction condition. Several ROP catalysts/initiators have been used to synthesize the polymer, among them metal-catalyzed polymerization using oxides, salts and complexes of Al, K, Ti, Zn, Zr, Sn and rare earths metals;

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

-catalyzed polymerization; and alcohol-initiated polymerization.

Physical properties

PTMC is a predominantly amorphous polymer in the relaxed state but it can present some crystallinity, particularly when the chains are stretched. The polymer presents

glass transition temperature The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rub ...

(

T_g

) between -15 to -30 °C and melting temperature (

T_m

) ranging from 38 to 41°C. Low molecular weight PTMC is a rubbery polymer with poor dimensional stability, tackiness, and inadequate mechanical properties. Nevertheless, high molecular weight amorphous PTMC (over 100,000) is very flexible, with a relatively low elastic modulus (5–7 MPa) at room temperature, tough and it presents excellent ultimate mechanical properties. Mechanical properties of the rubber can be also improved upon cross-linking by gamma-irradiation. PTMC has resistance to non-enzymatic hydrolysis, compared to most

aliphatic In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated, like hexane, ...

polyesters Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include natural ...

, but it is biodegradable ''in vivo'' by enzymes. It is a resorbable material since the ester bonds can be enzymatically broken, producing CO

_2

and water. So, ''in vivo'', it degrades by surface erosion and its decomposition products contain no organic acids, preventing potential inflammatory responses.

Applications

Due to the predominant amorphous nature, PTMC is a flexible polymer with rubbery behavior. In addition, the

biodegradability Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradati ...

and

biocompatibility Biocompatibility is related to the behavior of biomaterials in various contexts. The term refers to the ability of a material to perform with an appropriate host response in a specific situation. The ambiguity of the term reflects the ongoing de ...

of PTMC make it to have high applicability in biomedical applications as scaffolds for tissue regeneration and drug delivery devices. PTMC has been used as scaffolds for

tissue engineering Tissue engineering is a biomedical engineering discipline that uses a combination of cells, engineering, materials methods, and suitable biochemical and physicochemical factors to restore, maintain, improve, or replace different types of biolog ...

particularly for some types of soft tissues in which the maintenance of mechanical properties is important for tissue reconstruction. PTMC-based membranes have been also evaluated as barrier for use in hard tissue guided regeneration like bone. The performance of these membranes is comparable with commercial collagen and e-PTFE membranes, showing well suitability for use in guided bone regeneration. Due to rubbery and hydrophobic nature, PTMC-based copolymers produced from ROP of TMC with lactone-based comomers have been synthesized to modify these characteristics, amplifying applications. Thus, the use as resorbable medical devices in which control of rigidity and biodegradation time are desired has been proposed. Main examples of these copolymers are poly(L-lactide-co-trimethylene carbonate), poly(glycolide-''co''-trimethylene carbonate) and poly(caprolactone-''co''-trimethylene carbonate).{{Cite journal , last1=Rocha , first1=Daniela Nogueira , last2=Brites , first2=Pedro , last3=Fonseca , first3=Carlos , last4=Pêgo , first4=Ana Paula , date=Feb 2014 , title=Poly(Trimethylene Carbonate-co-ε-Caprolactone) Promotes Axonal Growth , journal=PLOS ONE , language=en , volume=9 , issue=2 , pages=e88593 , doi=10.1371/journal.pone.0088593 , issn=1932-6203 , pmc=3937290 , pmid=24586346, bibcode=2014PLoSO...988593R , doi-access=free Poly(L-lactide-co-trimethylene carbonate) has been proposed for application as small diameter vascular grafts. Poly(glycolide-''co''-trimethylene carbonate) is a commercial monofilament used for suture with slow biodegradation rate which allows maintenance of high mechanical strength compatible with the surgical recovery. Poly(caprolactone-''co''-trimethylene carbonate) has been proposed as biomaterial for conduits in the regeneration of central nervous system.

References

Carbonate esters Polycarbonates